1. Field of the Invention
This invention relates to cartridge-loaded film for use in motion picture cameras and the like, and in particular to film of the type wherein one film surface carries a raised stripe of sound recording material and a raised balance stripe.
2. Description Relative to the Prior Art
U.S. Pat. No. 3,208,686 entitled "Film Cartridge" and issued on Sept. 28, 1965 in the names of Mr. Evan A. Edwards et al discloses a "super 8" type film cartridge for use in motion picture cameras. Such a cartridge includes a supply chamber wherein a coreless roll of motion picture film is positioned around a stationary post such that the film may be unwound and advanced along a film path, past an exposure aperture and rewound onto a rotatable core in a takeup chamber of the cartridge.
It is also known to modify such a cartridge to provide for the recording of sound simultaneous with exposure of the film to scene light. In this regard, reference is made to U.S. Pat. No. 3,442,580 issued May 6, 1969 in the name of A. Winkler. Such a cartridge may be loaded with film having a photosensitive emulsion on one surface thereof and a raised stripe of magnetic sound recording material carried by the opposite film surface and disposed adjacent and generally parallel to one longitudinal edge of the film. To facilitate handling and winding of such film into a generally cylindrical roll thereof, a similarly-raised balance stripe may typically be disposed adjacent the opposite longitudinal film edge of the film surface that carries the sound recording stripe. Reference in this regard is made to U.S. Pat. No. 3,220,843 which issued on Nov. 30, 1965 to Mr. R. C. Lovick, et al.
In both of the above-mentioned cartridge arrangements, the film supply roll may exhibit a clockspringing tendency wherein, after winding, successive convolutions of the roll become displaced radially because the inherent resiliency of the film tends to urge the film to an unwound state. Such clockspringing may typically occur where the film is coreless, i.e., not wound around or attached to a central core, or is attached to a central core that is free to rotate with respect to the cartridge. The clockspringing of an unstriped film roll presents no undue difficulties, but a clockspring striped film may develop a "stepped" configuration tending to affect adversely the operation of the cartridge. That is to say: although a striped film is initially wound into a generally cylindrical roll having generally flat roll ends, later clockspringing (radial convolution movement) of the roll reduces the friction force existing between adjacent convolutions, thereby permitting relative axial slippage of such convolutions and producing a roll having stepped, rather than flat, end faces. If such stepping is of sufficient magnitude to cause a film edge of one convolution to become perched atop the stripe of an adjacent convolution, and if frictional contact between the convolutions is then re-established as by the clockspringing of additional convolutions or by the application of tension to the free end of the rolled strip, the stepped condition becomes essentially permanent because of the wedging action of the stripe. Because a stepped roll has a greater axial length than does an unstepped roll, a stepped roll may exert undue frictional force against the opposed walls of a cartridge supply chamber, especially since such walls are desirably spaced apart by a distance only slightly greater than the width of the film strip in order to minimize the overall cartridge size. Such frictional force may be sufficient to resist or prevent unwinding of the roll in the cartridge thereby resulting in unsatisfactory operation.
The above-cited application Ser. No. 336,142 describes a device for expanding the cartridge supply chamber in response to insertion of the cartridge in a camera, thereby relieving the frictional contact between the roll and the cartridge walls. Although useful, such a device requires additional cartridge structure and accompanying manufacturing expense. Stepping may also be prevented by winding the film roll on a spool having opposed side flanges that tend to restrict axial convolution movement. The use of such a spool in a cartridge of the aforementioned type requires undesirable enlargement of the cartridge in order to accommodate the spool flanges.